In U.S. Pat. No. 3,965,249 it is shown that hypochlorite ions may be decomposed to give gaseous oxygen by mixing a stream containing such ions with an unsupported catalyst. The combined stream containing both the catalyst and the hypochlorite ions is disclosed entering a tank. The combined stream flows through the tank, and exits from the tank as an effluent stream. The tank is shown to comprise a series of compartments separated by baffles such that the combined stream alternatively flows upwards and downwards within the tank.
In the process of the invention a liquid influent stream containing said reactant is continuously passed through a volume of a particulate catalyst that is sufficient to decompose said reactant to a desired concentration and the evolved gas rises to the surface of said liquid and disengages therefrom into a gas space above said liquid, thereby providing an effluent stream having said desired concentration of said reactant.
Where a gas rises through a liquid and disengages from the liquid at the surface of the liquid, it is possible that hydrodynamic instabilities are generated. The problems presented by these hydrodynamic instabilities are exacerbated by the presence of particulate solids, such as those present in a static bed of particulate catalyst. It is possible that a liquid may be prevented from flowing through a bed of particulate solids under the action of gravity due to these hydrodynamic instabilities.
Such hydraulic instability difficulties are liable to occur where the concentration of the reactant is such that decomposition of the reactant to the desired concentration would evolve large amounts of gas, for example more than 0.5 volumes of gas (at the pressure and temperature at which the decomposition is effected) per volume of liquid.
These hydrodynamic instability difficulties can be avoided by limiting the volume of gas that has to be disengaged from a given area of the liquid surface. Thus the process could be effected using a bed of catalyst of relatively large cross sectional area so that there is a large area of liquid surface above the catalyst bed from which the evolved gas can disengage. However the use of such relatively large cross section area catalyst beds is liable to give rise to the risk of back mixing of the effluent stream that has passed through the catalyst with the influent stream so that the concentration of the reactant in the effluent is not at the desired level.